ACI 211.2-98 (Repproved 2004) supersedes ACI 211.2-91 and became effective ACI 211.2-98 (Repproved 2004) supersedes ACI 211.2-91 and became effective March 1, 1998.
March 1, 1998.
Copyright © 1998, American Concrete Institute. Copyright © 1998, American Concrete Institute.
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211.2-1 ACI Committee Reports, Guides, Standard Practices, and
ACI Committee Reports, Guides, Standard Practices, and Commentaries are intended for guidance in planning, Commentaries are intended for guidance in planning, designing, executing, and inspecting construction. This designing, executing, and inspecting construction. This document is intended for the use of individuals who are document is intended for the use of individuals who are competent to evaluate the significance and limitations of its competent to evaluate the significance and limitations of its content and recommendations and who will accept content and recommendations and who will accept responsibility for the application of the material it contains. responsibility for the application of the material it contains. The American Concrete Institute disclaims any and all The American Concrete Institute disclaims any and all responsibility for the stated principles. The Institute shall not responsibility for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom.
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health and safety standards.
Standard Practice for Selecting Proportions for Structural
Standard Practice for Selecting Proportions for Structural
Lightweight Concrete (
Lightweight Concrete (A
ACI 211.2-98)
CI 211.2-98)
Reported by ACI Committee 211
Reported by ACI Committee 211
Edward A. Abdun-Nur Edward A. Abdun-Nur Stanley G. Barton* Stanley G. Barton* Leonard W. Bell Leonard W. Bell George R. U. Berg George R. U. Berg Stanley J. Blas, Jr. Stanley J. Blas, Jr. Peggy M. Carrasquillo Peggy M. Carrasquillo Ramon L. Carrasquillo Ramon L. Carrasquillo Martyn T. Conrey Martyn T. Conrey James E. Cook James E. Cook Russell A. Cook Russell A. Cook ** William A. Cordon William A. Cordon Wayne J. Costa Wayne J. Costa Kenneth W. Day Kenneth W. Day Calvin L. Dodl Calvin L. Dodl** Donald E. Graham Donald E. Graham George W. Hollon George W. Hollon** William W. Hotaling, Jr. William W. Hotaling, Jr. Robert S. Jenkins Robert S. Jenkins Paul Klieger Paul Klieger Frank J. Lahm Frank J. Lahm Stanley H. Lee Stanley H. Lee Gary R. Mass Gary R. Mass Richard C. Meininger Richard C. Meininger Richard W. Narva Richard W. Narva Leo P. Nicholson Leo P. Nicholson James E. Oliverson James E. Oliverson James S. Pierce James S. Pierce Sandor Popovics Sandor Popovics Steven A. Ragan Steven A. Ragan Harry C. Robinson Harry C. Robinson Jere H. Rose Jere H. Rose James A. Scherocman James A. Scherocman James M.
James M. Shilstone, Sr.Shilstone, Sr. George B. Southworth George B. Southworth Alfred B. Spamer Alfred B. Spamer Paul R. Stodola Paul R. Stodola** Michael A. Taylor Michael A. Taylor Stanley J. Virgalitte Stanley J. Virgalitte** William H. Voelker William H. Voelker Jack W. Weber Jack W. Weber Dean J. White, II Dean J. White, II Milton H. Wills, Jr. Milton H. Wills, Jr. Francis C. Wilson Francis C. Wilson Robert L. Yuan Robert L. Yuan *
*Members of Subcommittee B who prepared this standard.Members of Subcommittee B who prepared this standard.
ACI 211.2-98
ACI 211.2-98
(Reapproved 2004)
(Reapproved 2004)
This standard describes, with examples, two methods for This standard describes, with examples, two methods for propor-tioning and adjusting proportions of structural grade concrete tioning and adjusting proportions of structural grade concrete containing lightweight aggregates. The weight (pycnometer) method containing lightweight aggregates. The weight (pycnometer) method uses a specific gravity factor determined by a displacement uses a specific gravity factor determined by a displacement pycnom-eter test on the aggregates (Method 1). The weight method also eter test on the aggregates (Method 1). The weight method also employs the specific gravity factor to estimate the weight per yd employs the specific gravity factor to estimate the weight per yd 33of theof the fr
fresh esh conconcrcreteete. . The The damdamp, p, looloose se volvolume ume methmethod od useuses s the the cemecement nt content-strength relationship for the design of all
content-strength relationship for the design of all lightweight lightweight and sand and sand lightweight concrete (Method 2). Examples are given for systematic lightweight concrete (Method 2). Examples are given for systematic calculation of batch weights; effective displaced volumes; and calculation of batch weights; effective displaced volumes; and adjust-ment to compensate for
ment to compensate for changes in aggrechanges in aggregate moisture content; aggre-gate moisture content; aggre-gate proportions; cement content; slump, air content, or both
gate proportions; cement content; slump, air content, or both
Keywords:
Keywords: absorption; absorption; adsorptionadsorption; air content; air entrainment; cement; air content; air entrainment; cement content; coarse aggregate; fine aggregate; fineness modulus; grading; content; coarse aggregate; fine aggregate; fineness modulus; grading; light-weight aggregate;
weight aggregate; mixture proportioningmixture proportioning; moisture; slump test; specific; moisture; slump test; specific gravity factor.
gravity factor.
Committee that voted on reapproval, 2004
Committee that voted on reapproval, 2004
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Frank A. KozeliskiKozeliski Chair Chair Ed T. McGuire Ed T. McGuire Secretary Secretary G. Michael Robinson G. Michael Robinson Chair, Subcommittee B Chair, Subcommittee B
CONTENTS CONTENTS Chapter 1—Introduction, p. 211.2-2 Chapter 1—Introduction, p. 211.2-2 1.1 1.1 PurposePurpose 1.2 1.2 ScopeScope
Chapter 2—Factors affecting proportioning of
Chapter 2—Factors affecting proportioning of
lightweight-aggregat
lightweight-aggregate concrete, e concrete, p. 211.2-2p. 211.2-2
2.1
2.1 Aggregates (absorption and moisture content)Aggregates (absorption and moisture content) 2.2
2.2 AggregatesAggregates ( (gradation)gradation) 2.3
2.3 Water-cementitiWater-cementitious ous material ratiomaterial ratio 2.4
2.4 Air entrainmentAir entrainment
Chapter 3—Estimating first trial mixture
Chapter 3—Estimating first trial mixture
proportions, p. 211.2-4
proportions, p. 211.2-4
3.1
3.1 GeneralGeneral 3.2
3.2 Method 1: Weight method (specific gravity pycnometer)Method 1: Weight method (specific gravity pycnometer) 3.3
3.3 Method 2: Volumetric method (damp, loose volume)Method 2: Volumetric method (damp, loose volume)
Chapter 4—Adjusting mixture proportions,
Chapter 4—Adjusting mixture proportions,
p. 211.2-16
p. 211.2-16
4.1
4.1 GeneralGeneral 4.2
4.2 Method 1Method 1:: Weight method (specific gravity p Weight method (specific gravity pycnometer)ycnometer)
4.3
4.3 Method 2Method 2:: Volumetric method (damp, loose volume) Volumetric method (damp, loose volume) 4.4
4.4 Adjustment proceduresAdjustment procedures 4.5
4.5 Controlling proportions in the fieldControlling proportions in the field
Chapter 5—References, p. 211.2-18
Chapter 5—References, p. 211.2-18
5.1
5.1 Referenced standards and reportsReferenced standards and reports
Appendix A—Determination of specific
Appendix A—Determination of specific gravitygravity
factors of structural lightweight aggregate,
factors of structural lightweight aggregate,
p. 211.2-19
p. 211.2-19
Appendix B—Determination of structural
Appendix B—Determination of structural
light-weight coarse aggregate absorption, p. 211.2-20
weight coarse aggregate absorption, p. 211.2-20
CHAPTER 1—INTRODUCTION CHAPTER 1—INTRODUCTION 1.1—Purpose
1.1—Purpose
The purpose of this standard is to provide generally The purpose of this standard is to provide generally appli-cable methods for selecting and adjusting mixture cable methods for selecting and adjusting mixture propor-tions for structural lightweight concrete. These methods are tions for structural lightweight concrete. These methods are also applicable to concrete containing a combination of also applicable to concrete containing a combination of lightweight and normalweight aggregate.
lightweight and normalweight aggregate.
1.2—Scope 1.2—Scope
Discussion in this standard is limited to structural grade, Discussion in this standard is limited to structural grade, lightweight aggregates, and
lightweight aggregates, and structural lightweight-aggregatestructural lightweight-aggregate concrete. Structural lightweight-aggregate concrete is concrete. Structural lightweight-aggregate concrete is defined as concrete which: (a) is made with lightweight defined as concrete which: (a) is made with lightweight aggregates conforming to ASTM C 330, (b) has a co
aggregates conforming to ASTM C 330, (b) has a compressivempressive strength in excess of 2500 psi (17.2 MPa) at 28 days of age strength in excess of 2500 psi (17.2 MPa) at 28 days of age when tested in accordance with methods stated in ASTM C when tested in accordance with methods stated in ASTM C 330, and (c) has an equilibrium weight not exceeding 115 lb/ 330, and (c) has an equilibrium weight not exceeding 115 lb/ ft
ft33 (1842 kg/m (1842 kg/m33) as determined by ASTM C 567. Concrete in) as determined by ASTM C 567. Concrete in which a portion of the lightweight aggregate is replaced by which a portion of the lightweight aggregate is replaced by normalweight aggregate is within the scope of this standard. normalweight aggregate is within the scope of this standard. When normalweight fine aggregate is used, it should conform When normalweight fine aggregate is used, it should conform to the requirements of ASTM C 33. The use of pozzolanic and to the requirements of ASTM C 33. The use of pozzolanic and chemical admixtures is not covered in this standard.
chemical admixtures is not covered in this standard.
CHAPTER
CHAPTER 2—FA2—FACTORS AFFECTINGCTORS AFFECTING PROPORTIONING OF LIGHTWEIGHT PROPORTIONING OF LIGHTWEIGHT
AGGREGATE CONCRETE AGGREGATE CONCRETE
2.1—Aggregates (absorption and moisture content) 2.1—Aggregates (absorption and moisture content)
2.1.1
2.1.1 The principal factors necessitating modification of The principal factors necessitating modification of
proportioning and control
proportioning and control procedures for lightweight-aggregateprocedures for lightweight-aggregate concrete, compared with normalweight concrete, are the concrete, compared with normalweight concrete, are the greater absorptions and the higher rates of absorption of greater absorptions and the higher rates of absorption of most lightweight aggregates.
most lightweight aggregates. 2.1.2
2.1.2 Damp aggregates are preferable to dry aggregates at Damp aggregates are preferable to dry aggregates at time of mixing, as they tend to absorb less water during time of mixing, as they tend to absorb less water during mixing and therefore reduce the possibility of loss
mixing and therefore reduce the possibility of loss of slumpof slump as the concrete is being mixed, transported, and placed. as the concrete is being mixed, transported, and placed. Damp aggregates have less tendency to segregate in storage. Damp aggregates have less tendency to segregate in storage. Absorbed water is accounted for in the Absorbed water is accounted for in the mixture-propor-tioning procedure.
tioning procedure. 2.1.3
2.1.3 When concrete is made with lightweight aggregates When concrete is made with lightweight aggregates that have low initial moisture contents (usually less than 8 that have low initial moisture contents (usually less than 8 toto 10%) and relatively high rates of absorption, it may be 10%) and relatively high rates of absorption, it may be desir-able to mix the aggregates with one-half to two-thirds of the able to mix the aggregates with one-half to two-thirds of the mixing water for a short period before adding cement, mixing water for a short period before adding cement, admixtures, and air-entraining admixture to
admixtures, and air-entraining admixture to minimize slumpminimize slump loss. The supplier of the particular aggregate should be loss. The supplier of the particular aggregate should be consulted regarding the necessity for such predampening consulted regarding the necessity for such predampening and for mixing procedure.
and for mixing procedure. 2.1.4
2.1.4 Concrete made with saturated lightweight aggre- Concrete made with saturated lightweight aggre-gates may be more vulnerable to freezing and thawing than gates may be more vulnerable to freezing and thawing than concrete made with damp or dry lightweight aggregates, concrete made with damp or dry lightweight aggregates, unless the concrete is allowed to lose its excess moisture unless the concrete is allowed to lose its excess moisture after curing, before such exposure, and has developed after curing, before such exposure, and has developed adequate strength to resist
adequate strength to resist freezing.freezing. 2.1.5
2.1.5 When producing trial batches in When producing trial batches in the laboratory usingthe laboratory using the specific gravity method, the specific gravity of the the specific gravity method, the specific gravity of the light-weight aggregate should be determined at the moisture weight aggregate should be determined at the moisture content anticipated before use.
content anticipated before use. 2.1.6
2.1.6 For most concrete mixture proportions to be prac- For most concrete mixture proportions to be prac-tical, aggregate proportions should be listed at a moisture tical, aggregate proportions should be listed at a moisture condition readily attainable in the laboratory and in
condition readily attainable in the laboratory and in the field.the field. In structural lightweight concrete, the main problem is In structural lightweight concrete, the main problem is accounting properly for the moisture in (absorbed), and on accounting properly for the moisture in (absorbed), and on (adsorbed), the lightweight aggregate particles as well as for (adsorbed), the lightweight aggregate particles as well as for the effects of absorption for a
the effects of absorption for a specific application. Tradition-specific application. Tradition-ally, concrete technologists have assumed, for aggregate ally, concrete technologists have assumed, for aggregate moisture content correction purposes, that aggregates are in moisture content correction purposes, that aggregates are in one of the four conditions at the time of use. These four one of the four conditions at the time of use. These four conditions are shown in
conditions are shown in Fig. 2.1Fig. 2.1..
Most concrete mixture proportions are reported with Most concrete mixture proportions are reported with aggregates in either saturated surface-dry (SSD) condition or aggregates in either saturated surface-dry (SSD) condition or oven-dry (OD) condition. In the field, aggregates are usually oven-dry (OD) condition. In the field, aggregates are usually in the air-dry (AD) or wet
in the air-dry (AD) or wet condition. Lightweight aggregate,condition. Lightweight aggregate, however, usually presents a unique situation. Most structural however, usually presents a unique situation. Most structural lightweight-aggregate concrete mixture proportions are lightweight-aggregate concrete mixture proportions are reported in the OD condition; however, in the field they are reported in the OD condition; however, in the field they are not SSD, but in a damp or wet condition. This condition is not SSD, but in a damp or wet condition. This condition is usually achieved by sprinkling, soaking, thermal quenching, usually achieved by sprinkling, soaking, thermal quenching, or vacuum saturation. The result is sometimes referred to as or vacuum saturation. The result is sometimes referred to as the “as-is” condition
The main problem for the concrete technologist is to have an easy method of using field data to convert the oven-dry laboratory trial proportions to proportions in the “as-is” moisture condition.
2.2—Aggregates (gradation)
2.2.1 Grading of the fine and coarse aggregates and the proportions used have an important effect on the concrete. A well-graded aggregate will have a continuous distribution of particle sizes, producing a minimum void content and will require a minimum amount of cement paste to fill the voids. This will result in the most economical use of cement and will provide maximum strength with minimum volume change due to drying shrinkage.
2.2.2 In general, the largest total volume of aggregate in the concrete is achieved:
(a) when the coarse aggregate is well graded from the largest to the smallest sizes;
(b) when the particle is rounded to cubical in shape; and (c) when the surface texture is least porous.
Conversely, concrete containing coarse aggregates that tend to be angular in shape, more porous in surface texture, and possibly deficient in one or more particle sizes, will require a smaller volume of aggregates.
These same factors of grading, particle shape, and texture also affect the percentage of fine aggregate required with a minimum percentage of fine aggregate being associated with a rounded or cubical shape and smooth texture. It is common that when a well-graded, normalweight sand is used to replace lightweight fine aggregate, the proportion of coarse lightweight aggregate may be increased. The proportion of coarse aggregate should approach the maximum consistent with workability and placeability, unless tests indicated that a lesser proportion provides optimum characteristics.
In some cases, strength may be increased by reducing the nominal maximum size of the aggregate without increasing the cement content.
2.2.3 For normalweight aggregates, the bulk specific gravities of fractions retained on the different sieve sizes are nearly equal. Percentages retained on each size indicated by weight
give a true indication of percentages by volume. The bulk specific gravity of the various size fractions of lightweight aggregate, however, usually increases as the particle size decreases. Some coarse aggregate particles may float on water, whereas material passing a No. 100 sieve (0.15 mm) may have a specific gravity approaching that of normalweight sand. It is the volume occupied by each fraction, and not the weight of material retained on each sieve, that determines the void content and paste content, and influences workability of the concrete. For a fine aggregate with a specific gravity of 1.89, the percentages retained on each sieve and fineness modulus, by weight and by volume, are computed for comparison in the example illustrated in Table 2.1.
A fineness modulus of 3.23 by volume in the example indicates a considerably coarser grading than that normally associated with the fineness modulus of 3.03 by weight. Therefore, lightweight aggregates require a larger percentage of material retained on the finer sieve sizes on a weight basis than do normalweight aggregates to provide an equal size distribution by volume.
2.2.4 As indicated in Section 1.2, concrete containing some normalweight aggregates, such as normalweight sand, is classified as lightweight concrete, provided the strength and unit weight requirements are met. The use of normal-weight sand usually results in some increase in strength and modulus of elasticity. These increases, however, are made at the sacrifice of increased weight. The mixture proportions Fig. 2.2—“As-is” condition.
Fig. 2.1—States of moisture in aggregate.
Table 2.1—Comparison of fineness modulus by weight and volume for typical lightweight aggregate
Sieve size, no. Opening, in. (mm) Percent retained by weight Cumulative percent retained by weight Bulk specific gravity, SSD basis Percent retained by volume Cumulative percent retained by volume 4 0.187(4.75) 0 0 — 0 0 8 0.0937 (2.38) 22 22 1.55 26 26 16 0.0469 (1.19) 24 46 1.78 25 51 30 0.0234 (0.59) 19 65 1.90 19 70 50 0.0117 (0.30) 14 79 2.01 13 83 100 0.0059 (0.15) 12 91 2.16 10 93 Pan — 9 100 2.40 7 100
selected, therefore, should consider these properties in conjunction with the corresponding effects on the overall economy of the structure.
2.3—Water-cementitious material ratio
2.3.1 Method 1 Lightweight-aggregate concrete may be proportioned by Method 1 (weight method, specific gravity pycnometer) on the basis of an approximate water-cementi-tious material ratio (w / cm) relationship when the absorption of the lightweight aggregate is known or determined, as described later in Appendix A. This method utilizes the fact that the sum of the weights per unit volume of all ingredients in a mixture is equal to the total weight of the same mixture. If the weight of the particular concrete per unit volume, which contains a particular aggregate, is known or can be estimated from the specific gravity factor of the aggregate, the weight of the lightweight aggregates in that volume of concrete can be determined.
2.3.2 Method 2 When trial mixtures are proportioned by procedures other than the weight method (Method 1 specific gravity pycnometer), the net water-cement ratio of most lightweight concrete mixtures cannot be established with sufficient accuracy to be used as a basis for mixture proportioning. This is due to the difficulty of determining how much of the total water is absorbed in the aggregate and thus is not available for reaction with the cement, versus the amount of water that is absorbed in open surface pores or cells of the aggregate particles, which usually remains there after surface drying and is available to react with the cement. The amount of free water in the surface pores or open cells varies according to the size and number of pores or open cells in the lightweight-aggregate particles. Lightweight-aggregate concrete mixtures are usually established by trial mixtures proportioned on a cement air content basis at the required consistency rather than on a water-cement ratio-strength basis when the weight method is not employed.
2.4—Air entrainment
2.4.1 Air entrainment is recommended in most light-weight-aggregate concrete as it is in most normalweight concrete (ACI 201.2R and 213R). It enhances workability, improves resistance to freezing-and-thawing cycles and deicer chemicals, decreases bleeding, and tends to obscure minor grading deficiencies. When severe exposure is not anticipated, its use may be waived, but the beneficial effects of air entrainment on concrete w orkability and cohesiveness are desirable and can be achieved at air contents of not less than 4.0%. Entrained air also lowers the unit weight of the concrete by several percentage points.
2.4.2 The amount of entrained air recommended for light-weight-aggregate concrete that may be subjected to freezing-and-thawing or to deicer salts is 4 to 6% air when maximum aggregate size is 3/4 in. (19.0 mm), and 4.5 to 7.5% when maximum aggregate size is 3/8 in. (9.5 mm).
2.4.3 The strength of lightweight concrete may be reduced by high air contents. At normal air contents (4 to 6%), the reduction is small if slumps are 5 in. (125 mm) or less and cement contents are used as recommended.
2.4.4 The volumetric method of measuring air, as described in ASTM C 173/C 173M, is the most reliable method of measuring air in either air-entrained concrete or non-air-entrained, structural lightweight concrete and is recommended.
CHAPTER 3—ESTIMATING FIRST TRIAL MIXTURE PROPORTIONS
3.1—General
The best approach to making a first trial mixture of light-weight concrete, which has given properties and uses a particular aggregate from a lightweight-aggregate source, is to use proportions previously established for a similar concrete using aggregate from the same aggregate source. Such proportions may be obtained from the aggregate supplier and may be the result of either laboratory mixtures or of actual mixtures supplied to jobs. These mixtures may then be adjusted as necessary to change the properties or proportions using the methods described in Chapter 4.
Chapter 3 provides a guide to proportioning a first trial mixture where such prior information is not available, following which, the adjustment procedures of Chapter 4 may be used. Trial mixtures can be proportioned by either:
1. Method 1 (weigh t met hod, specif ic gravit y pycno-meter) Lightweight coarse aggregate and normalweight fine aggregate; or
2. Method 2 (volumetric method) All lightweight and combinations of lightweight and normalweight aggregates.
Method 1 (the weight method) is described in detail in Section 3.2, and the volumetric method is described in Section 3.3.
3.2—Method 1: Weight method (specific gravity pycnometer)
For use with lightweight coarse aggregate and normal-weight fine aggregate.
3.2.1 This procedure is applicable to sand-lightweight concrete comprised of lightweight coarse aggregate and normalweight fine aggregate. Estimating the required batch weights for the lightweight concrete involves determining the specific gravity factor of lightweight coarse aggregate, as discussed in Appendix A, from which the first estimate of the weight of fresh lightweight concrete can be made. Addition-ally, the absorption of lightweight coarse aggregate may be measured by the method described in ASTM C 127 or by the spin-dry procedure discussed in Appendix B, which permits the calculation of effective mixing water.
3.2.2 The proportioning follows the sequence of straight-forward steps that, in effect, fit the characteristics of the available materials into a mixture suitable for the work. The question of suitability is frequently not left to the individual who selects the proportions. The job specifications may dictate some or all of the following:
1. Minimum cement or cementitious materials content; 2. Air content;
3. Slump;
4. Nominal maximum size of aggregate; 5. Strength;
6. Unit weight;
7. Type of placement (such as pump, bucket, belt conveyor); and
8. Other requirements (such as strength overdesign, admixtures, and special types of cement and aggregate).
Regardless of whether the concrete characteristics are prescribed by the specifications or are left to the individual selecting the proportions, establishment of batch weights per unit volume of concrete can be best accomplished in the following sequence:
Step 1: Choice of slump If slump is not specified, a value appropriate for the work can be selected from Table 3.1. The slump ranges shown apply when vibration is used to consol-idate the concrete. Mixtures of the stiffest consistency that can be placed efficiently should be used.
Step 2: Choice of nominal maximum size of lightweight aggregate The largest nominal maximum size of well-graded aggregates has fewer voids than smaller sizes. Hence, concrete with large-sized aggregates require less mortar per unit volume of concrete. Generally, the nominal maximum size of aggregate should be the largest that is economically available and consistent with the dimensions of the structure. In no event should the nominal maximum size exceed one-fifth of the narrowest dimension between sides of forms, one-third the depth of slabs, nor three-quarters of the minimum clear spacing between individual reinforcing bars, bundles of bars, or pretensioning strands. These limitations are sometimes waived by the engineer if workability and methods of consolidation are such that the concrete can be placed without honeycombing or voids. When high-strength concrete is desired, better results may be obtained with reduced nominal maximum sizes of aggregate because these can produce higher strengths at a given w / c or w / cm.
Step 3: Estimation of mixing water and air content The quantity of water per unit volume of concrete required to produce a given slump is dependent on the nominal maximum size, particle shape and grading of the aggregates, amount of entrained air, and inclusion of chemical admix-tures. It is not greatly affected by the quantity of cement or cementitious materials. Table 3.2 provides estimates of required mixing water for concrete made with various nominal maximum sizes of aggregate, with and without air entrainment. Depending on aggregate texture and shape, mixing water requirements may be somewhat above or below the tabulated values, but they are sufficiently accurate for the first estimate. Such differences in water demand are
not necessarily reflected in strength because other compen-sating factors may be involved.
Table 3.2 indicates the approximate amount of entrapped air to be expected in non-air-entrained concrete, and shows the recommended levels of average air content for concrete in which air is to be purposely entrained for durability, work-ability, and reduced in weight.
When trial batches are used to establish strength relation-ships or verify strength-producing capability of a mixture, the least-favorable combination of mixing water and air content should be used. That is, the air content should be the maximum permitted or likely to occur, and the concrete should be gaged to the highest permissible slump. This will avoid developing an overly optimistic estimate of strength on the assumption that average rather than extreme conditions will prevail in the field. For additional information on air content recommendations, see ACI 201.2R, 213R, 302.1R, and 345R.
Step 4: Selection of approximate w / c—The required w / c or w / cm is determined not only by strength requirements but also by such factors as durability and finishing properties. Because different aggregates and cements generally produce
Table 3.1—Recommended slumps for various types of construction
Slump, in. (mm)* Types of construction Maximum† Minimum† Beams and reinforced walls 4 (100) 1 (25) Building columns 4 (100) 1 (25) Floor slabs 3 (75) 1 (25) *Slump may be increased when chemical admixtures are used, provided that the admixture-treated concrete has the same or lower w / c or w / cm and does not exhibit segregation potential or excessive bleeding.
†May be increased 1 in. for methods of consolidation other than vibration.
Table 3.2—Approximate mixing water and air content requirements for different slumps and nominal maximum sizes of aggregates*
Aggregate size (9.5 mm)3/8 in. (12. 7 mm)1/2 in. (19.0 mm)3/4 in. Air-entrained concrete
Water, lb/yd3 (kg/m3) of concrete Slump, 1 to 2 in. (25 to 50 mm) 305 (181) 295 (175) 280 (166) Slump, 3 to 4 in. (75 to 100 mm) 340 (202) 325 (193) 305 (181) Slump, 5 to 6 in. (125 to 150 mm) 355 (211) 335 (199) 315 (187)
Recommended average† total air content, %, for level of exposure Mild exposure 4.5 4.0 4.0 Moderate exposure 6.0 5.5 5.0 Extreme exposure‡ 7.5 7.0 6.0
Nonair-entrained concrete
Water, lb/yd3 (kg/m3) of concrete Slump, 1 to 2 in. (25 to 50 mm) 350 (208) 335 (199) 315 (187) Slump, 3 to 4 in. (75 to 100 mm) 385 (228) 365 (217) 340 (202) Slump, 5 to 6 in. (125 to 150 mm) 400 (237) 375 (222) 350 (208) Approximate amount of entrapped air in nonair-entrained concrete, %
3 2.5 2
*Quantities of mixing water given for air-entrained concrete are based on typical total contents requirements as shown for “moderate exposure” in the table above. These quantities of mixing water are for use in computing cement or cementitious materials content for trial batches at 68 to 77 °F (20 to 25 °C). They are maximum for reason-ably well-shaped angular aggregates graded within limits of accepted specifications. The use of water-reducing chemical admixtures (ASTM C 494) may also reduce mix-ing water by 5% or more. The volume of the liquid admixtures is included as part of the total volume of the mixing water. The slump values of 7 to 11 in. (175 to 275 mm) are only obtained through the use of water-reducing chemical admixture; they are for concrete containing nominal maximum size aggregate not longer than 1 in. (25 mm). †Additional recommendations for air content and necessary tolerances on air content for control in the field are given in a number of ACI documents, including ACI 201.2R, 345R, 318, 301, and 302.1R. ASTM C 94 for ready-mixed concrete also gives air con-tent limits. The requirements in other documents may not always agree exactly, so in proportioning concrete, consideration should be given to selecting an air content that will meet the needs of the job and also meet the applicable specifications.
‡These values are based on the criteria that 9% air is needed in the mortar phase of the concrete. If the mortar volume will be substantially different from that determined in this recommended practice, it may be desirable to calculate the needed air content by taking 9% of the actual mortar value.
different strengths at the same w / c or w / cm, it is highly desirable to have or develop the relationship between strength and w / c or w / cm for the materials actually to be used. In the absence of such data, approximate and relatively conservative values for concrete containing Type I portland cement can be taken from Table 3.3. With typical materials, the tabulated w / c or w / cm should produce the strengths shown, based on 28 day tests of specimens cured under standard laboratory conditions. The average strength selected must exceed the specified strength by a sufficient margin to keep the number of low tests within specified limits. For severe conditions of exposure, the w / c or w / cm should be kept low even though strength requirements may be met with a higher value. Table 3.4 gives limiting values.
Step 5: Calculation of cement content The amount of cement per unit volume of concrete is determined in Steps 3 and 4. The required cement is equal to the estimated mixing water content (Step 3) divided by the w / c (Step 4). If, however, the specification includes a separate minimum limit on cement in addition to requirements for strength and durability, the mixture must be based on whichever criterion leads to the larger amount of cement. The use of other cementitious materials or chemical admixtures will affect
properties of both the fresh and hardened concrete. The use of various combinations of cementitious material, use of chemical admixtures, or both, is beyond the scope of this document, but may be found in ACI 212.1R, 212.2R, 226.1R, and 226.3R.
Step 6 : Estimation of lightweight coarse aggregate content Aggregates of essentially the same nominal maximum size and grading will produce concrete of satisfac-tory workability when a given volume of coarse aggregate, on a dry, loose basis, is used per unit volume of concrete. Appropriate values for this aggregate volume are given in Table 3.5. For equal workability, the volume of coarse aggregate in a unit volume of concrete depends only on its nominal maximum size and fineness modulus of the normal-weight fine aggregate. Differences in the amount of mortar required for workability with different aggregates, due to differences in particle shape and grading, are compensated for automatically by differences in dry loose unit weight.
The volume of aggregate, in ft3 (m3), on an oven-dry loose basis, for a unit volume of concrete is equal to the value from Table 3.5 multiplied by 27 for a yd3 (1 for a m3). This volume is converted to dry weight of coarse aggregate required in a unit volume of concrete by multiplying it by the oven-dry loose weight per ft3 (m3)of the lightweight coarse aggregate.
Step 7 : Estimation of fine aggregate content At comple-tion of Step 6, all ingredients of the concrete have been esti-mated except the fine aggregate. Its quantity is determined by difference.
If the weight of the concrete per unit volume is estimated from experience, the required weight of fine aggregate is the difference between the weight of fresh concrete and the total weight of the other ingredients.
Often the unit weight of concrete is known with reason-able accuracy from previous experience with the materials. In the absence of such information, Table 3.6 can be used to make a first estimate based on the specific gravity factor of the lightweight coarse aggregate and the air content of the concrete. Even if the estimate of concrete weight per yd3 (m3) is approximate, mixture proportions will be sufficiently accurate to permit easy adjustment on the basis of trial batches, as will be shown in the examples.
The aggregate quantities to be weighed out for the concrete must allow for moisture in the aggregates. Gener-ally, the aggregates will be moist and their dry weights should be increased by the percentage of water they
Table 3.3—Relationships betweenw / c and
compressive strength of concrete*
Compressive strength at 28 days, psi (MPa)
Approximate water-cement ratio, by weight Nonair-entrained concrete Air-entrained concrete 6000 (41.4) 5000 (34.5) 4000 (27.6) 3000 (20.7) 2000 (13.8) 0.41 0.48 0.57 0.68 0.82 — 0.40 0.48 0.59 0.74
*Values are estimated average strengths for concrete containing not more than 2% air for non-air-entrained concrete and 6% total air content for air-entrained concrete. For a constant w/c or w / cm, the strength of concrete is reduced as the air content is increased. Twenty-eight-day strength values may be conservative and may change when various cementitious materials are used. The rate at which the 28-day strength is developed may also change.
Strength is based on 6 x 12 in. (150 x 300 mm) cylinders moist cured for 28 days in accordance with the sections on “Initial Curing” and “Curing of Cylinders for Check-ing the Adequacy of Laboratory Mixture Proportions for Strength or as the Basis for Acceptance or for Quality Control” of ASTM C 31 of Making and Curing Concrete Specimens in the Field . These are cylinders moist cured at 73.4± 3 °F (23± 2 °C) before testing.
The relationship in this table assumes a nominal maximum aggregate size of about 3/4 to 1 in. (19 to 25 mm) For a given source of aggregate, st rength produced at a given w / c or w / cm will increase as nominal maximum size of aggregate decreases. See Section 2.3.
Table 3.4—Maximum permissible water-cement ratios for concrete in severe exposures*
Type of structure
Structure wet continuously or frequently; exposed to
freezing and thawing†
Structure exposed to sea water or
sulfates Thin sections (railings, curbs,
sills, ledges, ornamental work) and sections with less than 1 in. (25 mm) cover over steel
0.45 0.40‡
All other structures 0.50 0.45‡ *Based on ACI 201.2R.
†Concrete should also be air entrained.
‡If sulfate-resisting cement (Type II or Type V of ASTM C 150) is used, permissible w/c or w / cm may be increased by 0.05.
Table 3.5—Volume of coarse aggregate per unit of volume of concrete*
Maximum size of aggregate, in. (mm)
Volume of oven-dry loose coarse aggregates* per unit volume of concrete for different fineness
moduli of sand 2.40 2.60 2.80 3.00 3/8 (9.5) 1/2 (12.7) 3/4 (19.0) 0.58 0.67 0.74 0.56 0.65 0.72 0.54 0.63 0.70 0.52 0.61 0.68 *Volumes are based on aggregates in oven-dry loose condition as described in ASTM C 29/C 29M for unit weight of aggregate. These volumes are selected from empirical relationships to produce concrete with a degree of workability suitable for usual rein-forced construction. For more workable concrete, such as may sometimes be required when placement is to be by pumping, they may be reduced up to 10%.
contain, both absorbed and surface. The mixing water added to the bath must be reduced by an amount equal to the free moisture contributed by the aggr egate (such as total moisture minus absorption).
3.2.3 Sample computations—Method 1: weight method (specific gravity pycnometer)— A sample problem in inch-pound units (Example A—inch-inch-pound units) will be used to illustrate application of the proportioning procedures. The following conditions are assumed:
3.2.3.1 Type I non-air-entrained cement will be used. 3.2.3.2 Lightweight coarse aggregate and normalweight fine aggregate are of satisfactory quality and are graded within limits of generally accepted specifications, such as ASTM C 330 and C 33.
3.2.3.3 The coarse aggregate has a specific gravity factor of 1.50 and an absorption of 11.0%.
3.2.3.4 The fine aggregate has an absorption of 1.0%, and a fineness modulus of 2.80.
Lightweight concrete is required for a floor slab of a multistory structure subjected to freezing and thawing during construction. Structural design considerations require a 28-day compressive strength of 3500 psi. On the basis of information in Table 3.1 and previous experience, under the conditions of placement to be used, a slump of 3 to 4 in. should be used and that the available 3/4 in.to No. 4 light-weight coarse aggregate will be suitable.
The oven-dry loose weight of coarse aggregate is found to be 47 lb/ft3. Employing the sequence outlined in Section 3.2.2, the quantities of ingredients per yd3 of concrete are calculated as follows:
Step 1 As indicated previously, the desired slump is 3 to 4 in.
Step 2 The locally available lightweight aggregate, graded from 3/4 in. to No. 4, has been indicated as suitable. Step 3 Because the structure will be exposed to severe weathering during construction, air-entrained concrete will be used. The approximate amount of mixing water to produce a 3 to 4 in. slump in air-entrained concrete with 3/4 in. nominal maximum-size aggregate is found from Table 3.2 to be 305 lb/yd3. Estimated total air content is shown as 6.0%.
Step 4 From Table 3.3, the w / c needed to produce a strength of 3500 psi in air-entrained concrete is found to be approximately 0.54. In consideration of the severe exposure during construction, the maximum permissible w / c or w / cm from Table 3.4 is 0.50.
Step 5 From the information derived in Steps 3 and 4, the required cement content is found to be 305/0.50 = 610 lb/yd3.
Step 6 The quantity of lightweight coarse aggregate is estimated from Table 3.5. For a fine aggregate having fine-ness modulus of 2.80 and 3/4 in. nominal maximum size of coarse aggregate, the table indicates that 0.70 yd3of coarse aggregate, on a dry-loose basis, may be used in each yd3of concrete. Therefore, for a unit volume, the coarse aggregate will be 1 × 0.70 = 0.70 yd3. Because it weighs 47 lb/ft3, the dry weight of coarse aggregate is 0.70 × 47 × 27 = 888 lb. Because the coarse aggregate has an absorption of 11.0%, the saturated weight is 1.11 × 888 = 986 lb.
Step 7 With the quantities of water, cement, and coarse aggregate established, the remaining material comprising the yd3 of concrete must consist of sand and the total air used. The required sand is determined on the weight basis by difference. From Table 3.6, the weight of a yd3 of air-entrained concrete made with lightweight aggregate having a specific gravity factor of 1.50 is estimated to be 2980 lb. (For a first trial batch, exact adjustments of this value for usual differences in slump, cement factor, and aggregate specific-gravity factor are not critical.) Weights already known are
The saturated surface dry (SSD) weight of sand, therefore, is estimated to be 2980 – 1901 = 1079 lb. Oven-dry weight of sand is 1079/1.01 = 1068 lb.
Step 8 For the laboratory trial batch, it is convenient to scale the weights down to produce at least 1.0 ft3 of concrete. The batch weights for a 1.0 ft3batch are calculated as follows
Tests indicate total moisture content of 15.0% for the lightweight coarse aggregate and 6. 0% for the fine aggregate. Absorbed water does not become part of the mixing water and must be excluded from the adjustment of added water. Thus, surface water contributed by the lightweight coarse aggregate amounts to 15.0 – 11.0 = 4. 0% and by the fine aggregate 6.0 – 1.0 = 5.0%. The adjustments to the aggregates for this free moisture are calculated as follows
Per yd3 Water (net mixing) 305 lb
Cement 610lb
Coarse aggregate 986 lb (saturated)
Total 1901 lb
Cement 610/27 = 22.59 lb
Fine aggregate (SSD) 1079/27 = 39.96 lb Coarse aggregate (SSD) 986/27 = 36.52 lb Water (net mixing) 305/27 = 11.30 lb
Total 110.37 lb
Table 3.6—First estimate of weight of fresh lightweight concrete comprised of lightweight coarse aggregate and normalweight fine aggregate
Specific gravity factor
First estimate of lightweight concrete weight, lb/yd3(kg/m3)* Air-entrained concrete 4% 6% 8% 1.00 1.20 1.40 1.60 1.80 2.00 2690 (1596) 2830 (1680) 2980 (1769) 3120 (1852) 3260 (1935) 3410 (2024) 2630 (1561) 2770 (1644) 2910 (1727) 3050 (1810) 3200 (1899) 3340 (1982) 2560 (1519) 2710 (1608) 2850 (1691) 2990 (1775) 3130 (1858) 3270 (1941) *Values for concrete of medium richness (550 lb of cement per yd3 [326 kg/m3]) and medium slump with water requirements based on values for 3 to 4 in. (75 to 100 mm) slump in Table 3.2. If desired, the estimated weight may be refined as follows, if necessary information is available: for each 10 lb (5.9 kg) difference in mixing water from Table 3.2, correct the weight per yd3 15 lb in the opposite direction (8.9 kg per m3); for each 100 lb (59.3 kg3) difference in cement content from 550 lb (326 kg), correct the weight per yd3 15 lb in the same direction (8.9 kg per m3).
The adjustment of the added water to account for the mois-ture added with the aggregates is as follows
Water from fine aggregate = 41.96 – 39.96 = 1.98 lb Water from coarse aggregate = 37.84 – 36.52 = 1.32 lb
Therefore, water to be added to the batch is 11.30 – 1.98 – 1.32 = 8.00 lb The weights to be used for the 1.0 ft3 trial batch are
Step 9 Although the calculated quantity of water to be added was 8.00 lb, the amount actually used in an attempt to obtain the desired 3 to 4 in. slump was 8.64 lb. The as-mixed batch, therefore, consists of
The concrete mixture is judged to be satisfactory as to workability and finishing properties; however, the concrete had a measured slump of only 2 in. and a unit weight of 108.0 lb/yd3. To provide the proper yield for future trial batches, the following adjustments are made.
Because the yield of the trial batch was 111.01/108.0 = 1.028 ft3 and the mixing water actually used was 8.64 (added) + 1.98 (from fine aggregate) + 1.32 (from coarse aggregate) = 11.94 lb, the mixing water required for 1 yd3 of concrete with the same 2 in. slump as the trial batch should be approximately
(11.94/1.028) × 27 = 314 lb
As indicated in Section 4.4.2.3, this amount must be increased by about 15 lb/yd3 to raise the slump from the measured 2 in. to the desired 3 to 4 in. range, bringing the net mixing water to 329 lb. With the increased mixing water, additional cement will be required to maintain the desired w / c of 0.50. The new cement content per yd3 becomes
329/0.50 = 658 lb
Because workability was found to be satisfactory, the quantity of lightweight coarse aggregate per unit volume of concrete will be maintained the same as in the trial batch. The amount of coarse aggregate per yd3 becomes
(37.84/1.028) × 27 = 994 lb (wet) which is
994/1.15 = 864 lb (dry) or
864 × 1.11 = 959 lb (SSD)
The new estimate for the weight (Fig. 4.1) of a unit volume of concrete is 108.0 × 27 = 2916 lb/yd3. Therefore, the amount of fine aggregate per yd3 required is
2916 – (329 + 658 + 959) = 970 lb (SSD) or
970/1.01 = 960 lb (dry) The adjusted batch weights per yd3 are
or on a SSD condition
A verification laboratory trial batch of concrete using the adjusted weights should be made to determine if the desired properties have been achieved.
3.2.6 Sample computations—Method 1: weight method (specific gravity pycnometer)—A second sample problem in inch-pound units. (Example B—inch-pound units) will be used to illustrate application of the proportioning procedures where several of the specific mixture requirements are speci-fied. Examples B and D (volumetric method—damp, loose volume method, Section 3.3.4) are similar for direct comparison of both methods.
Requirements
• 3500 psi specified compressive strength at 28 days; • 1200 psi required over-design (per ACI 318, Section
5.3.2.2, no prior history);
• Required average strength of concrete f cr ′ : 4700 psi; • Lightweight aggregate: ASTM C 330, 3/4 in. to No. 4; • Concrete sand: ASTM C 33, No. 4 to 0;
Fine aggregate (39.96/1.01)× 1.06 = 41.94 lb
Coarse aggregate (36.52/1.11)× 1.15 = 37.84 lb
Cement 22.59lb
Fine aggregate (wet) 41.94 lb Coarse aggregate (wet) 37.84 lb
Water (added) 8.00 lb
Total 110.37lb
Cement 22.59lb
Fine aggregate (wet) 41.94 lb Coarse aggregate (wet) 37.84 lb
Water (added) 8.64 lb
Total 111.01lb
Cement 658lb
Fine aggregate (dry) 960 lb Coarse aggregate (dry) 864 lb
Water (total*) 434 lb
Total 2916lb
Cement 658lb
Fine aggregate (SSD) 970 lb Coarse aggregate (SSD) 959 lb Water (net mixing) 329 lb
• Air-entraining admixture (AEA) for 6 ± 1%: ASTM C 260; • Water-reducing admixture (WRA) use permitted: ASTM C
494, Type A or D; and
• Slump: 4 ± 1 in.; conventional placement. Background information
From the lightweight-aggregate manufacturer:
• Specific gravity factor—1.48 at a 15% moisture content (ACI 211.2, Appendix A); and
• Suggested coarse aggregate factor (CAF) is 870 lb/yd3 at a 15% moisture content (“as-is” condition).
From the sand supplier:
• Specific gravity = 2.60, fineness modulus = 2.80. From the cement supplier:
• Specific gravity = 3.14; General information
• Moisture content at time of use = 15%; and • Unit weight of water = 62.4 lb/ft3.
Proportioning design
Step 1: Establish w / c required for 4700 psi air-entrained concrete = 0.42 (Table 3.4, interpolated value). Step 2: Establish water required per yd3 (SSD basis), 3
to 4 in. slump, air-entrained, 3/4 in. aggregate = 305 lb less 11% for WRA = 271 lb (Table 3.2). Step 3: Calculate cement content = 271 lb/0.42 = 645 lb. Step 4: Calculate air content = 27.00 ft3 /yd3 × 0.06 =
1.62 ft3.
Step 5: Calculate lightweight aggregate absolute volume
870 lb/1.48 × 62.4 lb/ft3 = 9.42 ft3.
Step 6: Calculate absolute volume of sand by totaling absolute volumes of all other materials and subtracting from 27 ft3.
Item A:Cement absolute volume = 645/3.14× 6.24 = 3.29 ft3
Item B: Water absolute volume = 271 lb/1 × 62.4 = 4.34 ft3 Item C: Air volume (from Step 4) = 1.62 ft3 Item D: Lightweight aggregate absolute volume
(from Step 5) = 9.42 ft3
Total of absolute volumes + volume of air 18.67 ft3 Item E: Sand absolute volume = 27.00 – 18.67 = 8.33 ft3 Sand weight = 8.33 × 2.60 × 62.4 = 1351 lb Step 7: Calculate theoretical plastic unit weight by
adding all batch weights and dividing by 27. Weights: 1 yd3
Cement 645 lb
LWA (as is) 870 lb
Sand (dry) 1351 lb
Water (total) 271 lb
Total 3137 lb/yd3
or 116.2 lb/ft3 plastic
Mixtures must be monitored and adjusted in the field to maintain yield.
3.25 Sample computations—Method 1: weight method (specific gravity pycnometer)— A sample problem in SI units (Example A—SI units) will be used to illustrate appli-cation of the proportioning procedures. The following conditions are assumed:
3.2.5.1 Type I non-air-entrained cement will be used. 3.2.5.2 Lightweight coarse aggregate and normalweight fine aggregate are of satisfactory quality and are graded within limits of generally accepted specifications, such as ASTM C 330 and C 33.
3.2.5.3 The coarse aggregate has a specific gravity factor of 1.50 and an absorption of 11.0%.
3.2.5.4 The fine aggregate has an absorption of 1.0%, and a fineness modulus of 2.80.
Lightweight concrete is required for a floor slab of a multistory structure subjected to freezing and thawing during construction. Structural design considerations require a 28-day compressive strength of 24 MPa. On the basis of information in Table 3.1 and previous experience, under the conditions of placement to be used, a slump of 75 to 100 mm should be used, and the available 19 to 5 mm lightweight coarse aggregate will be suitable.
The oven-dry loose weight of coarse aggregate is found to be 47 lb/ft3. Employing the sequence outlined in Section 3.2.2, the quantities of ingredients per yd3 of concrete are calculated as follows:
Step 1 As indicated previously, the desired slump is 75 to 100 mm.
Step 2 The locally available lightweight aggregate, graded from 19 to 5 mm, has been indicated as suitable.
Step 3 Because the structure will be exposed to severe weathering during construction, air-entrained concrete will be used. The approximate amount of mixing water to produce a 75 to 100 mm slump in air-entrained concrete with 19 mm nominal maximum-size aggregate is found from Table 3.2 to be 181 kg/m3. Estimated total air content is shown as 6.0%.
Step 4 From Table 3.3, the w / c needed to produce a strength of 24 MPa in air-entrained concrete is found to be approximately 0.54. In consideration of the severe exposure during construction, the maximum permissible w / c or w / cm from Table 3.4 is 0.50.
Step 5 From the information derived in Steps 3 and 4, the required cement content is found to be 181/0.50 = 362 kg/m3.
Step 6 The quantity of lightweight coarse aggregate is estimated from Table 3.5. For a fine aggregate having fine-ness modulus of 2.80 and 19 mm nominal maximum size of coarse aggregate, the table indicates that 0.70 m3of coarse aggregate, on a dry-loose basis, may be used in each m3of concrete. Therefore, for a unit volume, the coarse aggregate will be 1 × 0.70 = 0.70 m3. Because it weighs 753 kg/m3, the dry weight of coarse aggregate is 0.70 × 753 = 527 kg. Because the coarse aggregate has an absorption of 11.0%, the saturated weight is 1.11 × 527 = 585 lb.
Step 7 With the quantities of water, cement, and coarse aggregate established, the remaining material comprising the m3 of concrete must consist of sand and the total air used. The
required sand is determined on the weight basis by difference. From Table 3.6, the weight of a m3 of air-entrained concrete made with lightweight aggregate having a specific gravity factor of 1.50 is estimated to be 1768 kg. (For a first trial batch, exact adjustments of this value for usual differences in slump, cement factor, and aggregate specific-gravity factor are not critical.) Weights already known are
Therefore, the saturated surface dry (SSD) weight of sand is estimated to be 1768 – 1128 = 640 kg. Oven-dry weight of sand is 640/1.01 = 634 kg.
Step 8 For the laboratory trial batch, it is convenient to scale the weights down to produce at least 0.028 m3of concrete. The batch weights for a 0.028 m3batch are calculated as follows
Tests indicate total moisture content of 15.0% for the lightweight coarse aggregate and 6. 0% for the fine aggregate. Absorbed water does not become part of the mixing water and must be excluded from the adjustment of added water. Thus, surface water contributed by the lightweight coarse aggregate amounts to 15.0 – 11.0 = 4.0% and by the fine aggregate 6.0 – 1.0 = 5.0%. The adjustments to the aggregates for this free moisture are calculated as follows
The adjustment of the added water to account for the mois-ture added with the aggregates is as follows
Water from fine aggregate = 18.81 – 17.92 = 0.89 kg Water from coarse aggregate = 16.97 – 16.38 = 0.59 kg
Therefore, water to be added to the batch is 5.07 – (0.89 + 0.59) = 3.59 kg
The weights to be used for the 0.028 m3 trial batch are
Step 9 Although the calculated quantity of water to be added was 3.59 kg, the amount actually used in an attempt to obtain the desired 50 mm slump was 3.88 kg. Therefore, the as-mixed batch consists of:
The concrete mixture is judged to be satisfactory as to workability and finishing properties; however, the concrete had a measured slump of only 50 mm and a unit weight of 1730 kg/m3. To provide the proper yield for future trial batches, the following adjustments are made.
Because the yield of the trial batch was 49.80/1730 = 0.0288 m3 and the mixing water actually used was 3.88 (added) + 0.89 (from fine aggregate) + 0.59 (from coarse aggregate) = 5.36 kg, the mixing water required for 1 m3 of concrete with the same 50 mm slump as the trial batch should be approximately
(5.36/0.0288) = 186 kg
As indicated in Section 4.4.2.3, this amount must be increased by about 9 kg/m3 to raise the slump from the measured 50 mm to the desired 75 to 100 mm range, bringing the net mixing water to 195 kg. With the increased mixing water, additional cement will be required to maintain the desired w / c of 0.50. The new cement content per m3 becomes
195/0.50 = 390 kg/m3
Because workability was found to be satisfactory, the quantity of lightweight coarse aggregate per unit volume of concrete will be maintained the same as in the trial batch. The amount of coarse aggregate per m3 becomes
(16.97/0.0288) = 589 kg (wet) which is
589/1.15 = 512 kg (dry) or
512 × 1.11 = 569 kg (SSD)
The new estimate for the weight (Fig. 4.1) of a unit volume of concrete is 1730 kg/m3. Therefore, the amount of fine aggregate per yd3 required is
1730 – (195 + 390 + 569) = 576 kg (SSD) or
576/1.01 = 570 kg (dry) Per m3
Water (net mixing) 181 kg
Cement 362kg
Coarse aggregate 585 kg (saturated)
Total 1128kg
Cement 362 × 0.028 = 10.14 kg
Fine aggregate (SSD) 640 × 0.028 = 17.92 kg
Coarse aggregate (SSD) 585 × 0.028 = 16.38 kg
Water (net mixing) 181 ×0.028 = 5.07 kg
Total 49.51kg
Fine aggregate (17.92/1.01)× 1.06 = 18.81 kg
Coarse aggregate (16.38/1.11)× 1.15 = 16.97 lb
Cement 10.14kg
Fine aggregate (wet) 18.81 kg Coarse aggregate (wet) 16.97 kg
Water (added) 3.59 kg
Total 49.51kg
Cement 10.14kg
Fine aggregate (wet) 18.81 kg Coarse aggregate (wet) 16.97 kg
Water (added) 3.88 kg
The adjusted batch weights per m3 are
or on a SSD condition
A verification laboratory trial batch of concrete using the adjusted weights should be made to determine if the desired properties have been achieved.
3.2.6 Sample computations—Method 1: weight method (specific gravity pycnometer)—A second sample problem in SI units. (Example B-SI units) will be used to illustrate appli-cation of the proportioning procedures where several of the specific mixture requirements are specified. Examples B and D (volumetric method—damp, loose volume method, Section 3.3.4) are similar for direct comparison of both methods.
Requirements
• 24 MPa specified compressive strength at 28 days; • 8 MPa required over-design (per ACI 318, Section
5.3.2.2, no prior history);
• Required average strength of concrete f cr ′ : 32 MPa; • Lightweight aggregate: ASTM C 330, 19 to 5 mm; • Concrete sand: ASTM C 33, 5 to 0 mm;
• Air-entraining admixture (AEA) for 6 ± 1%: ASTM C 260; • Water-reducing admixture (WRA) use permitted:
ASTM C 494, Type A or D; and
• Slump: 100 ± 25 mm.; conventional placement. Background information
From the lightweight-aggregate manufacturer:
• Specific gravity factor—1.48 at a 15% moisture content (ACI 211.2, Appendix A); and
• Suggested coarse aggregate factor (CAF) is 516 kg/m3 at a 15% moisture content (“as-is” condition).
From the sand supplier:
• Specific gravity = 2.60, fineness modulus = 2.80. From the cement supplier:
• Specific gravity = 3.14. General information:
• Moisture content at time of use = 15%; and • Unit weight of water = 1000 kg/m3.
Proportioning design
Step 1: Establish w / c required for 32 MPa air-entrained concrete = 0.42 (Table 3.4, interpolated value).
Step 2: Establish water required per yd3 (SSD basis), 75 to 100 mm slump, air-entrained, 19 mm aggregate = 181 kg less 11% for WRA = 161 kg (Table 3.2). Step 3: Calculate cement content = 161 kg/0.42 = 383 kg. Step 4: Calculate air content = 0.06 m3.
Step 5: Calculate lightweight aggregate absolute volume
516/(1.48 × 1000) = 03.49 m3.
Step 6: Calculate absolute volume of sand by totaling absolute volumes of all other materials and subtracting from 1 m3.
Item A: Cement absolute volume = 383/(3.14 × 1000) = 0.122 m3 Item B:Water absolute volume = 161/(1.00× 1000) = 0.161 m3
Item C: Air volume (from Step 4) = 0.060 m3 Item D: Lightweight aggregate absolute volume
(from Step 5) = 0.349 m3
Total of absolute volumes + volume of air = 0.692 m3 Item E: Sand absolute volume = 1.000 – 0.692 = 0.308 m3 Sand weight = 0.308 × 2.60 × 1000 = 800 kg Step 7: Calculate theoretical plastic unit weight by
adding all batch weights. Weights: 1 m3
Cement 383kg
LWA(asis) 516kg
Sand(dry) 800kg
Water (total) 161 kg
Total 1860kg/m3
Mixtures must be monitored and adjusted in the field to maintain yield.
3.3—Method 2: Volumetric method (damp, loose volume)
For use with all lightweight aggregate or a combination of lightweight and normalweight aggregates.
3.3.1 Some lightweight aggregate producers recommend trial mixture proportions based on damp, loose volumes converted to batch weights. This procedure is applicable to all lightweight or to sand lightweight concrete comprised of various combinations of lightweight aggregate and normal-weight aggregate. The total volume of aggregates required, measured as the sum of the uncombined volumes on a damp, loose basis, will usually be from 28 to 34 ft3 /yd3 (1.04 to 1.26 m3 /m3). Of this amount, the loose volume of the fine aggregate may be from 40 to 60% of the total loose volume. Both the total loose volume of aggregate required and the proportions of fine and coarse aggregates are dependent on several variables; these variables relate to both the nature of the aggregates and to the properties of the concrete to be produced. Estimating the required batch weights for the lightweight concrete involves estimating cement content to produce a required compressive strength level. The aggre-gate producer should be consulted to obtain a closer approximation of cement content and aggregate
propor-Cement 390kg
Fine aggregate (dry) 570 kg Coarse aggregate (dry) 512 kg
Water (total*) 258 kg
Total 1730kg
Cement 390kg
Fine aggregate (SSD) 576 kg Coarse aggregate (SSD) 568 kg Water (net mixing) 196 kg
tions required to achieve desired strength and unit weight with the specific aggregate. When this information is not available, the only alternative is to make a sufficient number of trial mixtures with varying cement contents to achieve a range of compressive strengths, including the compressive strength desired.
3.3.2 Estimation of cement content The cement content-strength relationship is similar for a given source of light-weight aggregate but varies widely between sources. There-fore, the aggregate producer should be consulted for a close approximation of cement content necessary to achieve the desired strength. When this information is not available, the cement content can be estimated from the data in Fig. 3.1
3.3.3 Sample computations A sample problem (Example C) will be used to illustrate application of the proportioning procedure. Assume that a sand lightweight concrete with 4000 psi (27.6 MPa) compressive strength weighing no more than 105 lb/ft3 (1682 kg/m3), air dry (as in ASTM C 567), is required and will be placed by bucket at a 4 in. (100 mm) slump. The damp, loose unit weights for the coarse and fine lightweight aggregates have been determined as 47 and 55 lb/ft3 (753 and 881 kg/m3). The normalweight fine aggregate has been determined to weigh 100 or 102 lb/ft3 (1602 or 1634 kg/m3) in a SSD condition with 2% absorption.
Bulking caused by moisture on the aggregate surface, while of little significance with coarse aggregate, must be taken into account with fine aggregate when using the damp,
loose volume method. This is accomplished by increasing the volume of lightweight fine aggregate, usually in the range of 2 to 3%, depending on the typical condition of the aggregate as shipped. Normalweight fine aggregates can vary appreciably from different sources in the same general area and are best handled on the basis of dry, loose volumes plus moisture. The local lightweight-aggregate producer has been consulted and has recommended 580 lb (344 kg) of cement per yd3 (m3)with 17 ft3 (0.63 m3) if coarse light-weight aggregate, 5 ft3 (0.18 m3) of lightweight fine aggregate, and 9-1/2 ft3 (0.35 m3) if normalweight fine aggregates per yd3 (m3). A trial batch of 1 ft3 (0.028 m3) will be made. The tabulated computations are as follows
First trial batch weights, damp,
loose, lb Adjusted weights, yd 3 damp, loose, lb Cement Coarse lightweight aggregate Fine lightweight aggregate Fine normalweight aggregate 580 27 --- = 21.5 27 1.011 --- ×21.5 = 574 17 ×47 27 --- = 29.6 27 1.011 --- ×29.6 = 791 5 ×55 27 --- = 10.2 27 1.011 --- ×10.2 = 272 9.5 ×102 27 --- = 35.9 27 1.011 --- ×35.9 = 959
Fig. 3.1 Relationship of compressive strength and cement content of field concrete for lightweight fine aggregate and coarse aggregate, or lightweight coarse aggregate and normalweight fine aggregate (data points represent actual project strength results using a number of cement and aggregate sources).
